Abstract

The thermal and photo-oxidative stabilisation of high styrene–butadiene copolymer (SBC) with high styrene content (K-Resin) has been studied using a variety of analytical and spectroscopic methods including yellowness, luminescence and FT-IR spectroscopy coupled with hydroperoxide analysis in order to understand the nature and effectiveness of the processes involved. The next stage of the program was to evaluate the effects of various chemical/solvent treatments on the role of metal ions/residual catalysts and hydroperoxides in the thermal and photostabilisation of SBS as well as combinations of phenolic antioxidants and phosphites/phosphonites. Other additives, such as HALS and a metal deactivator, were also added to the combinations of phenolic and phosphite antioxidants in order to study their behaviour and efficiency. The chemical treatments appeared to stabilise SBS against thermal oxidation to a greater or lesser extent. Phosphoric acid treatment via reflux and zinc dithiocarbamate treatments showed better performances than the rest of the treatments, the latter was particularly effective at inhibiting the discolouration. During photo-oxidation, on the other hand, chemical treatments involving phosphoric acid and pre-thermal effects showed the importance of catalyst effects. The addition of phenolic antioxidants, phosphites/phosphonites, metal deactivator and HALS was found to stabilise the SBS against thermal and photo-oxidation. In thermal oxidation, the combination of Irganox ® 1010/Irgafos ® 168 was found to effectively stabilise the polymer when the finalisation of the polymerisation was with adipic acid. When the same antioxidants were used, but with polymer finalised with BHT, strong yellowing was observed and a higher amount of hydroperoxides and oxidation products. Increasing the amount of antioxidants did not increase the stabilisation efficiency. The stabilisation efficiency of Irganox ® 1010 combined with Alkanox ® P-24 was found to be more effective than when it was combined with Irgafos ® 168. The formulations containing Irgafos ® 168/Irganox ® 1010 and Irgafos ® 168/Irganos ® 1330 were more effective in colour protection and retarding the formation of oxidation products than the combinations of Irgafos ® 168/Irganox ® 3114 and Irgafos ® 168/Lowinox ® 1790. The effect of the addition of HALS, such as Tinuvin ® 770, Tinuvin ® 622 and Chimassorb ® 944, and a metal deactivator, such as Irganox ® MD 1024, to the combination of Irgafos ® 168/Irganox ® 1010 was found to be antagonistic. In photo-oxidation, a combination of Irganox ® 1010/Irgafos ® 168 protected the polymer efficiently, when the polymerisation of the polymer was finalised with adipic acid. When the polymerisation was finalised with BHT, a higher amount of hydroperoxides and oxidation products was found. An increase in the amount of antioxidants did not enhance the stability of the polymer. The addition of Alkanox ® P-24 exhibited an opposite effect to that seen in thermal oxidation, as the stabilisation efficiency was less effective than with Irgafos ® 168. The formulation containing Irgafos ® 168/Irganox ® 1010 was found to be the most efficient compared with the other phenolic antioxidants. The addition of Tinuvin ® 770 to the formulation Irgafos ® 168/Irganox ® 1010 was found to have a synergistic effect. The addition of polymeric HALS or Irganox ® MD 1024, a metal deactivator, had an antagonistic effect on the stabilisation of the polymer. Disruption of the excimer sites in the styrenic phase also correlated with stabilisation effects.